1. Field of the Invention
This invention generally relates to woven preforms and particularly relates to woven preforms used in bonding of components at structural joints.
2. Description of the Related Art
When joining components in a structural joint, layers of fabric infused with a polymer resin can be used to join the components. For example, two components are brought to the desired positions and orientation, and layers of composites are adhered to the outer surfaces of the components: one portion of the fabric adhering to one component, another portion adhering to the other component. Multiple layers of fabric are stacked to increase the strength of the joint and to form a desired radius of curvature at the intersection.
While this method works, the joint can be improved by having fibers that extend through the intersection of the components, connecting the composite layers on both sides of the joint. A three-dimensional (3-D), woven, textile preform provides for fibers that extend through the intersection of a joint. The preform is infused with a resin that is cured to form a rigid polymer matrix surrounding the fibers of the preform.
Weave patterns for woven composite textiles have been used in the past which can provide for various shapes of three-dimensional preforms. However, these weave patterns were typically single-layer connectors, for example, U.S. Pat. No. 4,671,470 to Jonas, in which is disclosed an H-shaped connector for connecting a wing spar to a sandwich skin structure. Also, three-dimensional preforms have been woven to fill gaps formed during layup of composite layers into tight radius intersections. A gap-filling preform is disclosed in U.S. Pat. No. 5,026,595 to Crawford, Jr., et al.
However, these prior-art preforms have been limited in their ability to withstand high out-of-plane loads, to be woven in an automated loom process, and to provide for varying thickness of portions of the preform. Weave construction and automation of preform weaving was in its infancy and provided only a small advantage over conventional laminated, fiber-wound, or braided composites, limiting the versatility of the preforms.
There is a need for an improved preform having a modified weave architecture, providing the preform with symmetrical load-carrying ability and symmetrical load distribution. In addition, there is a need for an improved preform having a modified taper and weave sequence for forming the taper. Also, there is a need for a preform having tracer fibers for identifying selected portions of the preform or selected locations of the preform.